Technical summary

Gum Bichromate is not an inherently difficult process. With practice
and patience successful prints can be produced. Only one chemical is required
to produce the light sensitive emulsion, and prints are developed in water.
Nor is a light-tight workspace required; coating and developing can be undertaken
under subdued household lighting conditions.

A word of caution is to highlight the differences between published
sources of information on gum printing — perhaps due to the very flexibility
that gum printing offers. There is no right way to print gum — different
approaches and methods arise from the different results individual practioners
seek.

The flexibility of gum means that you can choose to make graphic images in
one colour, or you can seek to make three-colour images, or perhaps you prefer
(as I do) to create layers of multiple colour on the one image. All these
approaches are valid, however each will influence your working methods in
different ways — the key is to find the working method that reflects
your individual vision.

The information contained on these pages details my way of working,
which has evolved from ten years working with gum. It is not the only way
to print gum, but it is the way that works for me and the printmaking outcomes
I desire. Your needs may be different and you should explore and investigate
as much material as you need. I have suggested a variety of sites to visit
and the resources section lists
suggested books and other sources of information.

Gum printing variables

The skill in making gum prints is learning how to combine a variety
of variables, which range from sourcing an appropriate choice of paper (or
alternative support) and its preparation, through to the combination of gum
and pigment, sensitiser proportion and exposure and development. These numerous
variables can lead to frustration — but often the potential for prints
of exquisite beauty. Patience and persistence will deliver results.

The sections below detail the key variables in gum printing. Understanding
them will assist you to master the process.

Paper

Working with historical processes gives you the freedom to work with a broad
range of papers as well as other supports such as fabric, glass and metals.
My preference is to work with paper, and gum can be printed on a variety of
paper surfaces. Key points to consider in choosing paper include;

Single coated gum prints usually lack depth and contrast, with many people
choosing to work with multiple coatings — this requires papers that
can handle a significant degree of physical handling and multiple soakings

Papers need a degree of dimensional stability to enable accurate registration
between coats.

As the gum emulsion is hardened from the top down the chosen paper requires
enough 'tooth' to allow the hardened gum and pigment to adhere to the paper

Negatives

Gum printing in common with most historical processes is a contact printing
process, requiring that the negative is the same size as the final print.
Unless you work with a camera producing an 8" x 10" or larger negative,
working with gum will necessitate producing an enlarged negative the size
of the desired finished print. There are several routes to making enlarged
negatives, either working with traditional wet darkroom materials, or using
a digital workflow.

Pigments & gum arabic

The colour in gum prints comes from the use of pigment which is combined
with the gum arabic. Traditionally watercolour paints are used, though dry
pigments can also be used. Some practioners also work with inks or gouache
paints.

Gum arabic, a thick viscous syrup, can either be made from dry gum
arabic or it can be purchased ready-made from art supply stores. There is
much debate in gum circles about the best gums to work with. It is also possible
to use PVA adhesive rather than gum arabic.

Sensitiser & development

Two different dichromate sensitisers are commonly used, ammonium and
potassium dichromate. Ammonium is faster and prints with less contrast, while
potassium is slower and more contrasty. Further control can be achieved through
the ratio of sensitiser to gum/pigment. Choice of dichromate will also be
influenced by your printing lights and negatives.

The standard development method is to use 'automatic' development,
which involves developing the print for 30 mins in tepid water. However physical
development, which involves using brushes, water jets and other methods can
be used to alter tones, brush away details or make other changes to the print.

Printing lights & exposure

Like other historical processes, gum requires a strong UV light source
for exposure. Suitable light sources include the sun, fluorescent light boxes,
metal halide and mercury vapour lamps. Choice of sensitiser, negatives and
emulsion mix can all have an influence on the light source most suitable for
your working process.

Reflections on the Art and Science of Gum Bichromate Katharine Thayer's site provides a detailed analysis of gum printing,
debunking many of the common myths, and offering a valuable discussion on
pigments.

Christina's site offers excellent examples of contemporary 3 colour
gum printing and a well-illustrated 'learning' section which addresses a variety
of key questions for gum printers. You can also purchase her book 'Alternative
Processes Condensed'.